(1) Field of the Invention
The present invention relates to a noise reducing apparatus comprising an interference type hollow body for reducing incident sound from a sound source by interference.
(2) Related Art Statement
As a method for lowering the noise level of the sound emitted from a noise source, there has hitherto been widely carried out a method of surrounding the noise source with a shielding structure lined with a sound insulating material to reduce noise by an acoustic absorbing treatment and a sound insulating treatment.
There has also widely been used a method of preventing propagation of noises by providing a high sound shielding wall for lowering the noise level.
However, the prior method of shielding sound cannot be applied to such a portion as an engine room of a vehicle which requires a vent for radiating heat.
Moreover, if a sound shielding wall is provided in the engine of an aeroplane emitting a sound by an exhaust stream, an air flow becomes turbulent to cause an obstacle in suction and exhaust of air. Accordingly, such sound cannot be shielded.